= (+)206 (kj mol 1) 206 scores 1 only Units not essential if ans in kj mol 1 but penalise incorrect units

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Willa Lewis
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1 M.(a) (i) ΔH = Σ(enthalpies formation products) Σ(enthalpies formation reactants) Or correct cycle with enthalpy changes labelled = ( ) = (+)206 (kj mol ) 206 scores only Units not essential if ans in kj mol but penalise incorrect units (ii) ΔS = Σ(entropies of products) Σ(entropies reactants) = ( ) = (+) 26 (J K mol ) OR 0.26 kj K mol Units not essential but penalise incorrect units When ΔG = 0 OR ΔH = TΔS T = ΔH / ΔS M2 also scores M = / 26 Allow error carried forward from (a)(i) and (a)(ii) Ignore unexplained change of sign from to + = 954 K Allow , Units of K essential, must be +ve If values from (a)(i) and (a)(ii) lead to negative value in M3 allow M to M3 but do not allow negative temperature for M4 If negative value changed to positive for M4, allow M4 (c) To speed up the rate of reaction OR wtte Page 2

2 Allow so that more molecules have energy greater than the activation energy IF T in > 300 allow answers such as; to reduce energy cost to slow down reaction do NOT allow to increase rate (d) (i) Method ΔG = ΔH TΔS ΔG = 4 ( / 000) (M) If 42 and not 42 / 000 used can score M3 only but allow ΔG = (300 42) (M) = +3.6 kj mol =3600 J mol (M2) Units essential ΔG must be negative for the reaction to be feasible. OR ΔG is positive so reaction is not feasible Method 2 For reaction to be feasible ΔG must be negative or zero T when ΔG = 0 = ΔH / ΔS = 976K ΔS is ve so ΔG must be +ve at temperatures above 976K / at 300 K (ii) If the temperature is lowered (Ignore reference to catalyst and / or pressure) Alternative mark scheme (if T is calculated) Allow T reduced to 976 K or lower M ΔG will become (more) negative because the TΔS term will be less positive / TΔS>ΔH At this temperature (the reaction becomes feasible because) ΔG < = 0 M2 Page 3

3 [5] M2.(a) ΔS = = 80 J K mol ΔG = ΔH TΔS = 49 = +45. kj mol Units essential When ΔG = 0, ΔH = TΔS therefore T = ΔH / ΔS = / 80 = 272 (K) Mark consequentially to ΔS in part (a) (c) Diagram marks Diagram of a molecule showing O H bond and two lone pairs on each oxygen Page 4

4 Labels on diagram showing δ+ and δ- charges Allow explanation of position of δ+ and δ- charges on H and O Diagram showing δ+ hydrogen on one molecule attracted to lone pair on a second molecule Explanation mark Hydrogen bonding (the name mentioned) is a strong enough force (to hold methanol molecules together in a liquid) [0] M3.(a) An electron pair on the ligand Is donated from the ligand to the central metal ion Blue precipitate Dissolves to give a dark blue solution [Cu(H 2O) 6] NH 3 Cu(H 2O) 4(OH) 2 + 2NH 4 + Cu(H 2O) 4(OH) 2 + 4NH 3 [Cu(NH 3) 4(H 2O) 2] OH + 2H 2O Page 5

5 (c) [Cu(NH 3) 4(H 2O) 2] H 2NCH 2CH 2NH 2 [Cu(H 2NCH 2CH 2NH 2) 2(H 2O) 2] NH 3 (d) Cu N bonds formed have similar enthalpy / energy to Cu N bonds broken And the same number of bonds broken and made (e) 3 particles form 5 particles / disorder increases because more particles are formed / entropy change is positive Therefore, the free-energy change is negative M2 can only be awarded if M is correct [] M4.(a) Enthalpy change / ΔH when mol of a gaseous ion Enthalpy change for X + / - (g) X + / - (aq) scores M and M2 forms aqueous ions Allow heat energy change instead of enthalpy change Allow mol applied to aqueous or gaseous ions If substance / atoms in M CE = 0 If wrong process (eg boiling) CE = 0 ΔH(solution) = ΔH(lattice) + Σ(ΔHhydration) OR +77 = ΔH(hydration, Cl - ) OR ΔH(hydration, Cl - ) = Allow any one of these three for M even if one is incorrect Page 6

6 = 364 (kj mol ) Allow no units, penalise incorrect units, allow kj mol Allow lower case j for J (Joules) +364 does not score M2 but look back for correct M (c) Water is polar / water has Hδ+ (Chloride ion) attracts (the H in) water molecules (note chloride ion can be implied from the question stem) Idea that there is a force of attraction between the chloride ion and water Do not allow H bonds / dipole dipole / vdw / intermolecular but ignore loose mention of bonding Do not allow just chlorine or chlorine atoms / ion Mark independently (d) ΔG = ΔH TΔS Look for this equation in part (d) and / or (e); equation can be stated or implied by correct use. Record the mark in part (d) (ΔG = 0 so) T = ΔH / ΔS T = / 33 = 2333 K (allow range 2300 to ) Units essential, allow lower case k for K (Kelvin) Correct answer with units scores M, M2 and M3 2.3 (K) scores M and M2 but not M3 Above the boiling point of water (therefore too high to be sensible) / water Page 7

7 would evaporate Can only score this mark if M3 >373 K (e) ΔS = (ΔH ΔG) / T OR ΔS = (ΔG ΔH) / T = (( 5 + 9) 000) / 298 OR ( 5 + 9) / 298 = 20 J K mol OR kj K mol (allow 20 to 20.2) (allow to ) Answer with units must be linked to correct M2 For M3, units must be correct Correct answer with appropriate units scores M, M2 and M3 and possibly M in part (d) if not already given Correct answer without units scores M and M2 and possibly M in part (d) if not already given Answer of 240 / 0.24 means temperature of 25 used instead of 298 so scores M only If ans = +20 / assume AE and look back to see if M and possibly M2 are scored [3] Page 8

Page 2. (b) Mg 2+ (g) + 2e + 2Cl(g) (1) (M5)

Page 2. (b) Mg 2+ (g) + 2e + 2Cl(g) (1) (M5) M.(a) The enthalpy change / heat energy change / ΔH for the formation of one mole of (chloride) ions from (chlorine) atoms Allow enthalpy change for Cl + e Cl Do not allow energy change ionisation energy